1. Field of the Invention
The invention relates to compatible polyblends (polymer blends) comprised of two disparate polymethacrylates and/or polyacrylates.
2. Discussion of the Background
Decades ago, the experience with the miscibility of disparate polymers was summarized thusly: "In polyblends miscibility is the exception and immiscibility is the rule." (Dobry, A. and Boyer-Kawenoki, F., 1947, J. Polym. Sci., 2: 90.) In the meantime a number of systems comprised of disparate polymers have been described which formally satisfy the criteria of miscibility; however, such systems remain exceptions which "confirm the rule". (See Olabisi, O., Robeson, L. M., and Shaw, M. T., 1979, "Polymer-polymer miscibility", pub. Academic Press; and 1982 "Kirk-Othmer encyclopedia of chemical technology", 3rd Ed., Vol. 18, 443-478, pub. John Wiley.
For example, Olabisi et al., loc. cit., 233-238, have summarized the results with polyacrylates as follows: "Accumulated experience indicates that the members of the acrylate family are not miscible; and the same is true of the systems PMMA/polymethyl arylate and PMMA/polyethyl acrylate. (See Hughes, L. J., and Britt, G. E., 1961, J. Appl. Polym. Sci., 5: 337; and Hughes, L. J., and Brown, G. L., ibid., 580.)"
However, the following are miscible: (i) blends of polystyrene and poly-alpha-methylstyrene, at particular mixture ratios; (ii) blends of particular methyl-substituted polystyrenes, which display compatibility at temperatures above 180.degree. C. (Sillescu et al., 1986, Makromol. Chem. Rapid Commun., 7: 415-419); and (iii) blends of polyvinyl acetate and polymethylacrylate, or polyisopropyl acrylate and polyisopropyl methacrylate (see Krause, S., 1972, J. Macromol. Sci., Rvs. Macromol. Chem., C7, (2): 251-314).
There is some occurrence of miscibility in instances where special interactions, such as hydrogen bridge bonds, electron donor-acceptor complexes, etc., may develop between the disparate polymers. Examples which may be cited are: polystyrene/polyvinyl methyl ether; polystyrene/polyphenylene oxide; polystyrene/tetramethylpolycarbonate; PVC/PMMA; and polyvinylidene fluoride/PMMA ("PVDF/PMMA"). Due to the specific interactions between the monomer units in these polymers, the above-named blends display "lower critical solution temperature" (LCST) behavior. (See "Kirk-Othmer", 3rd Ed., loc. cit. Vol. 18, pp. 451-457.) The occurrence of an LCST, and a UCST (upper critical solution temperature), is expected based on theoretical considerations (Flory theory, and lattice theory), but the important chi parameter which characterizes the interaction must be obtained experimentally. It is not predictable. The relevant statement in Kirk-Othmer (p. 456) reads: "Thus the interaction parameter function cannot be derived from lattice considerations alone and the theory neither provides the understanding of the origin of the observed behavior nor possesses any quantitative predictive capacity."
There is a strong practical interest in polymer blends, particularly in miscible polymer systems, because these yield, for example, the mechanical qualities of the starting polymers, without being subject to phase separation and additive diffusion, which may occur under shear stress. (See "Kirk-Othmer", loc. cit., 449; and Olabisi, O., et al., loc. cit., 287-316.)
In "Kirk-Othmer", loc. cit., 451, it is stated that the concept of "complementary dissimilarity" (see also Olabisi, O., 1975, Macromolecules, 8: 316) explains the compatibility of fairly well studied "polymer blends" and has proven valuable as a heuristic principle.
Thus, the above-mentioned examples of compatible polyblends can largely be explained in terms of enthalpic interactions between the component units within polymer P1, and the component units within polymer P2.
For example, the compatible polyblend tetramethyl bisphenol A polycarbonate/polystyrene is accounted for in terms of electron donor-acceptor complex formation (see Barlow, J. W., and Paul, D. R., 1981, Annu. Rev. Mater. Sci., 299-319).
In addition there is a large group of compatible polyblends wherein the compatibility is based on an intramolecular repulsion within a copolymer. This group of polyblends includes, for example, the blend PMMA/styrene-acrylonitrile copolymer. In connection with this repulsion concept it is readily understood that miscibility will be found for a narrowly specific composition of the copolymer; thus the term "miscibility windows" is employed. Here also, exothermic miscibility has been recently discovered (Pfennig, J.-L. G., et al., 1985, Macromolecules, 18: 1937-1940). As discussed in unpublished Ger. Pat. App. P 36 38 443.7, this repulsion concept is also applicable to blends of homopolymers. Thus, the compatibility of PVDF/PMMA can be explained in terms of repulsion of the --CH.sub.2 -- and --CF.sub.2 -- groups in PVDF, and repulsion forces between ##STR3## and the carbonyl group in PMMA.
The compatibility in all of the above-mentioned compatible polyblends is ultimately attributable to various specific interactions between very disparate polymers P1 and P2. In the area of poly(meth)acrylates, the accumulated experience indicates little prospect of success in the search for compatible polyblends, because one can expect no specific interactions between two polymers of the same kind.